Observation of MeV-energy ions from the interaction of over picosecond laser pulses with near-critical density foam targets

In order to enhance the conversion efficiency of ultra-intense laser energy into plasma leading to ion acceleration, we have performed an experiment with over-picosecond laser pulses having a relativistic intensity interacting with foam targets. We adjust the prepulse of the laser to control the plasma density near the critical density. The combination of hydrodynamic and particle-in-cell simulations suggest that the region of high energy density is induced in the near-critical plasma, leading to enhance the proton energy up to 23 MeV with the laser intensity of 6 × 1018 W/cm2.